228 
Journal of Agricultural Research 
Vol. XXVIII, No. 3 
Chaetospermum glutinosum (Blanco) Swingle was quite easily infected both in 
the greenhouse and field in the absence of wounds. In fact, natural infection 
from adjoining plants in the field frequently occurred. Judging from its suscep¬ 
tibility under southern Alabama conditions, it is as susceptible as some of the 
Citrus fruits. However, these plants can not grow in southern Alabama as they 
are very easily killed by the winter temperatures generally prevailing in this region. 
Of the remaining plants belonging to the sub tribe Aeglinae, Balsamocitrus dawei 
Stapf and Aeglopsis chevalieri Swingle remained free from infection after repeated 
attempts to infect, while Aegle marmelos Correa, although infected at wounds 
on the leaves in the greenhouse, remained nonsusceptible in the field. 
Feronia limonia (Correa) Swingle was infected to some extent at wounds in 
the greenhouse. No results were obtained in the field. In the case of Feroniella 
lucida Swingle, however, positive results were obtained both in the greenhouse 
and field. • 
On the plants in sub tribe Lavanginae, two species, Triphasia trifolia (Burm.) 
P. Wilson and Severinia buxifolia Ten. proved to be strictly nonsusceptible in 
the field and greenhouse, while Paramignya monophylla Wight was easily in¬ 
fected in the greenhouse. Likewise, plants of Hesperethusa crenulata (Roxb.) 
Roem. were easily infected in the greenhouse and field through natural infection 
from adjoining plants. 
In the case of Severinia buxifolia it was repeatedly observed that the 
leaves, petioles, and stems when punctured or wounded had the ability to form 
cork tissues very rapidly. Owing to the nonsusceptibility of Severinia buxifolia 
to citrus canker and the fact that it thrives under southern Alabama conditions, 
its propagation as a hedge plant to replace Poncirus trifoliata (L.) Raf. should 
be encouraged. Incidentally, it may prove suitable as a stock for some types 
of Citrus fruits. 
All plants of the subtribe Citrinae were successfully infected, but in varying de¬ 
grees. Attempts to infect Citropsis schweinfurthii Swingle and M. Kellerman in 
the field were unsuccessful, although small unruptured spots were produced at 
wounds in the greenhouse. The two species of Atalantia have been rather 
easily infected. Likewise, plants of Eremocitrus glauca (Lindl.) Swingle were 
quite easily infected both in the greenhouse and field. 
The three species and one variety of Microcitrus and Eremocitrus glauca 
have proved susceptible enough under controlled conditions to be naturally 
infected in their native habitat, if a source for infection was present. Both of 
these genera are native of the east coast of Australia, and while citrus canker 
has only been reported from the northern territory of Australia, should canker 
be introduced at any time into the Citrus districts of Queensland, there is a bare 
possibility that citrus canker might be disseminated to the native growths of 
Microcitrus and Eremocitrus. 
Fortunella hindsii (Oliver) Sw T ingle is rather susceptible; much more so than 
any of the other three species of kumquats. While these were all successfully 
infected in the greenhouse, only two, F. japonica (Thunb.) Swingle and F. Mar¬ 
garita (Thunb.) Swingle gave positive results in the field. 
In the spring of 1918, thirty 3-year-old trees of Fortunella margarita budded 
on Poncirus trifoliata were planted in the isolation field. From the summer 
of 1918 through the season of 1921, not a single canker spot was found on these 
trees, notwithstanding the fact that various methods of inoculations were tried 
and that during the active growing season they were at all times exposed to natural 
infection. The kumquats, with the exception of F. hindsii are highly resistant 
to Citrus canker and it is only under the most favorable field conditions and 
through wounds on the leaves that they can be infected. 
In conclusion, it might be stated that so far as the menace of citrus canker 
to the Citrus industry in the United States is concerned, with the exception of 
Poncirus trifoliata , none of the relatives of Citrus, native or introduced, discussed 
